Bag manufacture



April 8., 1930- E. o. BARsTow ET AL BAG MANUFACTURE Filed Nov. 9, 1925 Patented Apr. 8, 11930 UNITED STATES PATENT OFFICE EDWIN 0. BARSTOW AND ARTHUR C. WHITE, OF MIDLAND, MICHIGAN, ASSIGNORS TO THE DOW CHEMICAL COMPANY, OF MIDLAND, MICHIGAN, A CQRPORATION OF MICHIGAN BAG MANUFACTURE Application filed November 9, 1925. Serial No. 67,785.

In the packaging yof granular products which are 'affected by moisture, while 1t 1s convenient to place such products in bags, the material of whichsuch bags are madenmust necessarily be substantially Water or moisture proof. Pitch constitutes an excellent waterproofing material for use in this connection, but the inclusion of such pitch in the wall. ot a bag or like container presents obvious duticulties. The interior of the bag must of course have a clean smooth surface and it is equally objectionable for the pitch to be on the outer surface. of the bag must be sufficiently stout to w1thstand rough handling where the bag 1s of the usual size and the packaged commodity a relatively heavy one, such, for example, as granular calcium chloride. C

The object of the present invention, accordingly, is the provision of a composite sheet for use in making moisture proof containers such as bags, which sheet will include a sufficiently heavy coating of pitch to render the same much more nearly impervious to moisture than any heretofore devised. At the same time, the coating of pitch is so applied and protected by additional layers of material as not to inj uriousl y affect either the inner or outer surface of the resultant composite sheet.

To the accomplishment of the foregoing and related ends, the invention then consists of the means hereinafter described and particularly pointed out in the clain'is, the an nexed drawing, and the following description setting forth but several of the various ways in which the principle vof the invention may be utilized.

In said annexed drawing Fig. l is a transverse section on an enlarged scale of one form of our present improved composite sheet; and Fig. 2 is a similar sec- .tion of another form of such sheet.

Referring first of all to the form of sheet illustrated in Fig. l, we utilize a layer (l) of hurlap as the intermediate layer of the com posite sheet. This burlap is thoroughly impregnated with pitch of the grade usually employed for waterproofing purposes, suficient pitch being emnloved in this connection At the same time the wall impregnated to leave a substantial film (2) thereof on either side ol the `burlap layer.

Protective layers and 4) of paper are then applied to the respective sides of said intern'iet'liate layer (l) and caused to adhere thereto b v passing the layers in assembled condition through-.a heated calender or otherwise subjecting same simultaneously to heat and pressure. Y

lf a sheet of greater thickness is desired, and the corresponding increased stiffness is not objectionable, a second protective layer of paper (not shown) may be applied to either side of the sheet as shown in Fig. l, being caused to adhere to the previously applied protective sheet (3 or 4), as the case may be, b v an interposed coating of pitch or equivalent adhesive waterproofing compound.

Burlap may be taken as typical of various loosely woven fabrics that may be employed as the intermediate pitch-impregnated layer in our improved sheet. Thus, as illustrated in Fig. 2, we employ for such intermediate layer a sheet of scrim. As before, the pitch wherewith such scrim is impregnated forms aI film ((3) on either side thereof and protective layers (7) and (8) are caused te adhere to such sides. which is designed for the outer face of the finished bag or container, is here made of burlap. Such burlap is desirable because of its strength as the outer layer of the package and we have found that it may he satisfactorily employed in conjunction with a pitch intermediate layer withoutdanger that the pitch will penetrate through the burlap which would be objectionable and is very apt to occur if the pitch be directly applied in adequate amount to the sheet of burlap as heretofore has been done.

The intermediate, loosely woven fabric layer, whether of burlap, scrim, or other material, may be satisfactorily impregnated in various ways to give the results hereinbefore described. For example, the sheet of fabric may be passed through a bath of pitch maintained at such a temperature as to give it the necessary degree of fluidity; or, the pitch may be sprayed onto the fabric from one or both sides; or the fabric may be passed over a roll Layer 8, however,.

that dips into a. bath of the pitch and carries a sufficient layer thereof into contact with the fabric to thoroughly impregnate the same and leave a residual film of the pitch on both sides thereof.

In conclusion, We should note that a pitch suitable' for -use in the manufacture of our improved bag material is that derived from petroleum stills, but that so-called asphalt pitch is also found satisfactory; while in place of `such a pitch proper, other equivalent adhesive and more or less Waterproof compounds may be employed in like manner, such, for example, as oxidized oils, like boiled linseed oil, or Chinawood oil. Casein, glue, and other types of adhesives, such as are used in making wood veneer products, may also be employed. The term pitch as used herein will accordingly be understood to connote all of these various equivalent materials.

Other forms may be employed embodying the features of our invention instead of the one here explained, change being made in the form or construction, provided the elements stated by any of the following claims or the equivalent of such stated elements be employed.

Ve therefore particularly point out and distinctly claim as our invention l. As a new article of manufacture, a composite sheet for use in making moisture-proof containers such as bags, such sheet including an intermediate layer of scrim impregnated with pitch and a layer of burlap and one of paper, not thus impregnated, adherent to the respective sides ofsaid intermediate layer.

2. A moisture-proof bag made from a sheet including an intermediate layer of scrim imprcgnated with pitch, and a layer of burla and one of paper, not thus impregnated, a herent to the outer and inner sides, krespectively, of said intermediate layer.

Signed by us this 6th day of November,

EDWIN O. BARSTOW. ARTHUR C. WHITE. 

